1. Field of the Invention
The present invention relates to an air-conditioning apparatus in which the quantity of refrigerant flow is controlled by electric expansion valves that are provided in a refrigerating cycle arrangement driven by an inverter compressor. In particular the present invention relates to a multi-room type air-conditioning apparatus having one outdoor apparatus and two or more indoor apparatuses with different capacities respectively that are connected to the outdoor apparatus.
2. Description of the Related Art
In a conventional multi-room type air-conditioning apparatus with two indoor apparatuses connected to one outdoor apparatus, there are provided expansion valves respectively corresponding to the indoor apparatuses. The expansion valves mentioned above are controlled with respect to the degree that the refrigerant obtained by the corresponding heat exchangers overheat which are respectively provided in the indoor apparatuses.
FIG. 1 shows the schematic constitution of a conventional two-room type air-conditioner. In FIG. 1, noted line arrow marks denote the flow of the refrigerant when the air-conditioner is driven for air-cooling operations and solid line arrow marks denote the flow of the refrigerant when the air-conditioner is driven for air-heating operations. That is to say, when the air-conditioner is driven for air-cooling, the refrigerant vapor compressed by a compressor 1 is fed to an outdoor heat exchanger 3 through a four-way valve 2 and the vapor is condensed and liquefied. The liquefied refrigerant is fed to a receiver tank 4 and stored therein. Subsequently, the pressure of the refrigerant fluid is reduced through electric expansion valves 6a and 6b respectively connected to the indoor apparatus A and B. The decompressed refrigerant is fed to the indoor heat exchangers 7 and 8 respectively in a state of decompressed vapor. The decompressed vapor in the heat exchangers 7 and 8 returns to the compressor 1 through a branch pipe 18 and through the four-way valve 2. In this cooling operation, the opening/closing degree of the electric valves 6a and 6b are respectively controlled by control signals g and h that are generated by an expansion valve controller (see FIG. 2) in such a manner that the temperature differences (TS-TA), (TS-TB) between the temperatures (TA) and (TB) are made constant. The temperatures (TA) and (TB) are detected by temperature sensors 16a and 16b attached to the exhaust pipes of the respective expansion valves 6a and 6b and the temperature (TS) is detected by a temperature sensor 9 attached to an inhalation pipe of the compressor 1.
When the air-conditioner is driven for air-heating operations, the direction of the flow of the refrigerant is reversed with respect to the direction in the cooling operation and the refrigerant vapor compressed by the compressor 1 is fed to the indoor heat exchangers 7 and 8 and is liquefied. The liquefied refrigerant is fed to the receiver tank 4 and the pressure of the refrigerant is reduced through an expansion valve 5 for heating. Subsequently the decompressed refrigerant is vaporized in the outdoor heat exchanger 3 and the refrigerant vapor returns to the compressor 1. In this heating operation, the opening/closing degree of the expansion valve 5 for heating is controlled by an output signal i of the expansion valve controller (see FIG. 2) so that the temperature difference (TS-TC) between the temperature (TC) detected by a temperature sensor 17 attached to the exhaust pipe of the expansion valve 5 and the temperature (TS) detected by a temperature sensor 9 attached to an inhalation pipe of the compressor 1 is made constant.
As described above, in the cooling and heating cycles of the conventional air-conditioner, the opening and closing degree of the heating expansion valve 5 and of the electric expansion valves 6a and 6b are controlled so that the temperature difference between the temperature of the exhaust refrigerant of the expansion valves 5, 6a and 6b and the temperature of the inhalation refrigerant to the compressor 1 is made constant. Thereby, the refrigeration cycle is merely stabilized. Even though the loads of the indoor apparatuses A and B are respectively varied, but a constant total for the sum of both loads is kept, the quantities of the refrigerant fluid flowing through the respective indoor heat exchangers 7 and 8 are varied so scarcely that the capability of the air-conditioner is generally stabilized. Moreover, the quantities of the loads (TRa-TIa) and (TRb-TIb) obtained by the differences between the set room temperatures (TRa) and (TRb) and the actually detected room temperatures (TIa) and (TIb) are used merely to determine the frequency f of the output signal of the compressor 1 as shown in FIG. 2.
However the conventional control method of the expansion valve, since the determination of the output of the compressor and the stabilization of the refrigeration cycle are independently performed when the two indoor apparatuses are driven at the same time, and a constant total for the sum of the loads of the respective indoor apparatuses is kept, even though the load of one of the indoor apparatuses is small and the load of the other is large, the quantity of the refrigerant flow into the respective indoor heat exchangers are generally equally divided. Therefore the refrigerating capability of the respective apparatus may be made generally equal.